The report notes that thousands of foreign fighters appear to have travelled to Afghanistan as the Islamic State’s physical caliphate in Syria and Iraq has unravelled in the face of counter-offensives by the Western-backed Iraqi government and the Russian-backed Syrian government.

Sky’s sources would not confirm whether any British citizens were thought to be present among the foreign fighters, but suggested they represented a “broad demographic”.

The Islamic State’s franchise in the region — named IS-Khorasan, after the loosely defined historic term of the Islamic empire beyond Persia’s eastern mountains — is something of a rival power structure to the Taliban which governed the country and sheltered al-Qaeda until 2001, and this is part of the reason Britain has upped its troop numbers in Afghanistan, at the request of the United States.

The Taliban itself has been offered “unconditional talks” on a peace deal by the Western-backed leadership in Afghanistan recently — a development celebrated as a positive move by Britain’s deputy ambassador to the country after years of failing to bring the Islamist group to heel and build a competent government.